1. Field of the Invention
The present invention relates to a capacitance type sensor suitably used for detecting a force applied from outside.
2. Description of the Related Art
A capacitance type sensor is in general use as a device for converting magnitude and direction of a force applied by an operator into electric signal. For example, a device having the capacitance type sensor for inputting operation of multidimensional direction incorporated as a so-called joystick is used as an input device of a mobile phone.
A capacitance type sensor can be used to input an operation having a specified dynamic range as a magnitude of a force applied by an operator. It can also be used as a 2-dimensional or 3-dimensional sensor capable of dividing an applied force into dimensional components, for force detection.
Reference is herein made for example to International Application No. PCT/JP00/09355 under the Patent Cooperation Treaty filed on Dec. 27, 2000 by the same applicant. It describes a capacitance type sensor 501 as shown in FIG. 11. The capacitance type sensor 501 has a substrate 520, a detective member 530 which is an operating member to which a force is applied from outside by a user, a displacement electrode 512 having conducting properties, capacitance element electrodes E501-E505 and a reference electrode (a common electrode) E500 formed on the substrate 520, an insulating film 513 formed to be laid over the substrate 520 so as to be closely contacted with the capacitance element electrodes E501-E505 and the reference electrode E500, and a supporting member 560 for fixedly supporting the detective member 530 and the displacement electrode 512 on the substrate 520.
As shown in FIG. 12, the capacitance element E505 of a circular form with center at the origin O, the capacitance element electrodes E501-E504 of a sector form arranged around it, and the reference electrode E500 of an annular form with center at the origin O arranged further around them are formed on the substrate 520. The capacitance element is formed between the displacement electrode 512 and the respective capacitance element electrode E501-E505.
In this capacitance type sensor 501, signals such as dock signals are input to the capacitance element electrodes E501-E505. When the detective member 530 is displaced by a force applied from outside in the condition in which the signals are being input to the capacitance element electrodes E501-E505, the displacement electrode 512 is displaced in a Z-axis direction in response to the displacement. Then, the distances between the electrodes of the capacitance elements formed between the displacement electrode 512 and the respective capacitance element electrodes E501-E505 vary and thereby the capacitance value of those capacitance elements change as the variations of the distance between the electrodes, to thereby produce a phase lag in the signals input to the capacitance element electrodes E501-E505. By using this phase lag in the input signals, the displacement of the detective member 530, i.e., the magnitude and direction of the force applied from outside to the detective member 530 in directions of X-axis, Y-axis, and Z-axis, are detected.
In the capacitance type sensor 501, when the detective member 530 is modified in shape, the capacitance variation property of the capacitance element varies in relation to an operating force applied to the detective member 530, so that operationality of the capacitance type sensor 501 used as the joystick varies. Accordingly, when the capacitance type sensor 501 is incorporated in the equipment such as a mobile phone and a personal digital assistant (PDA), each time the equipment is remodeled, the control circuit and software must be readjusted in consideration of the operationality as the joystick.
Also, in the capacitance type sensor 501, the displacement electrode 512 and the substrate 520 forming thereon the capacitance element electrodes E501-E505 are manufactured separately and then assembled together. Accordingly, the sensor cannot operate as the joystick until the assembly of the capacitance type sensor 501 is completed and thus the performance cannot be inspected before that.